Pipe bending machine with bending mandrel having a load bearing structure which is particularly resistant to working stresses

ABSTRACT

A pipe bending machine with bending mandrel having a load bearing structure which is particularly resistant to working stresses, comprises an extractor ( 2 ) which is fixed in a rear portion of the pipe bending machine, and mandrel rod ( 13 ) which extends with its longitudinal axis (g), from the extractor beyond a front portion of the machine, where a bending head ( 7 ) which is provided with a die ( 8 ) stresses a pipe (T) to be bent, which is inserted in a mandrel ( 12 ), by a traction resultant force that is transmitted along the mandrel rod ( 13 ) to the extractor ( 2 ) that counteracts with a resultant restraining reaction. The pipe bending machine comprises a load bearing structure ( 1 ) having a profile such that it contains inside the longitudinal axis (g) of the mandrel rod ( 13 ), in such a way that the load bearing structure ( 1 ) is subjected mainly to compression stresses.

TECHNICAL FIELD

The present invention relates to a pipe bending machine with bending mandrel having a load bearing structure which is particularly resistant to working stresses.

BACKGROUND ART

It is known that in a pipe bending machine with bending mandrel, an extractor is fixed in a rear portion of a machine workbench, and a mandrel rod extends longitudinally from the extractor beyond a front portion of the machine where are situated a mandrel and a bending head which is provided with a die. In the existing bending machines the workbench is fixed on a structure that is generally fixed to a floor.

When a pipe to be bent, which is inserted in the mandrel, is clamped onto the bending head die, a traction force that is applied tangentially to the bending head die causes on the mandrel a reaction directed along the mandrel rod, which is locked to the extractor in an end thereof opposite to the mandrel.

In the existing pipe bending machines with bending mandrel, the machine workbench is subjected substantially to bending stresses as a result of the force applied by the bending die over the machine workbench. These bending stresses, that propagate at an end of the machine structure from the bending die to the pipe to be bent and, in turn, from the latter to the mandrel and the mandrel rod, and again to the machine workbench through the extractor, in its end opposite to the end in which the mandrel rod is restrained, determine repeated elastic deformations on the workbench that cause warping of the structure. When the bending stresses become particularly heavy, especially in dependence on a material, a diameter and a thickness of the pipe to be bent, the elastic deformations become so high that they are no longer allowable if one wants to achieve a good quality of work and product.

DISCLOSURE OF INVENTION

This invention aims to overcome these drawbacks.

In particular, an object of the present invention is to manufacture a structure for a pipe bending machine with bending mandrel that is not subjected to bending stresses, when a pipe to be bent is subjected to a traction force by a bending head die.

Such an object and others are achieved by a pipe bending machine with bending mandrel having a load bearing structure which is particularly resistant to working stresses, in which an extractor is fixed in a rear portion of the pipe bending machine and mandrel rod extends with its longitudinal axis, from the extractor beyond a front portion of the machine, where a bending head which is provided with a die stresses a pipe to be bent, which is inserted in a mandrel, by a traction resultant force that is transmitted along the mandrel rod to the extractor that counteracts with a resultant restraining reaction, the pipe bending machine comprising a load bearing structure having a profile such that it contains inside the longitudinal axis of the mandrel rod, in such a way that the load bearing structure is subjected mainly to compression stresses.

The above mentioned pipe bending machine is particularly advantageous as said machine, since it is not subjected to bending stresses, does not undergo in its load bearing structure deformations that worsen its working way and damage its product.

Since it is the same load bearing structure that balances the tangential force applied to the die, the pipe bending machine discharges substantially only its load on a floor, thereby it needs no anchoring to the soil to prevent its deformation and increase its statics.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will be described with reference to its preferred embodiments, with connection to the enclosed drawings, in which:

FIG. 1 is a perspective view of a first embodiment of a pipe bending machine having a load bearing structure according to the present invention;

FIG. 2 is a schematic longitudinal cross section of the pipe bending machine in FIG. 1;

FIG. 3 shows an enlarged detail of a right-hand end of the pipe bending machine in FIG. 2;

FIG. 4 shows an enlarged detail of a left-hand end of the pipe bending machine in FIG. 2;

FIG. 5 shows an enlarged transversal cross section of the load bearing structure of the pipe bending machine in FIG. 1;

FIG. 6 shows a cross-sectioned perspective view of a second embodiment, that is circular, of a bearing structure of the pipe bending machine according to the present invention;

FIG. 7 shows a perspective view of a third embodiment, that is reticular, of a load bearing structure of the pipe bending machine according to the present invention; and

FIG. 8 shows a general perspective view of the third reticular embodiment of a load bearing machine without the pipe bending machine.

EXPLANATION OF THE PREFERRED EMBODIMENTS

Firstly, reference is made to FIGS. 1 and 2, in which a first embodiment of a load bearing structure of a pipe bending machine with bending mandrel according to the present invention is shown in a perspective view and in a schematic longitudinal cross section, respectively, is shown. In FIGS. 1 and 2, a first embodiment of load bearing structure, which is prismatic or box-shaped, is designed as 1. In a rear end of the load bearing structure 1 (at left hand in FIG. 2) an extractor is generally indicated as 2, and a front end (at right hand in FIG. 2) has a front frame 3.

The bearing structure 1 is sustained rear and in front on supporting elements 4 and 5 respectively. Suitably the front supporting element 5 projects forward with a step 6, on which a bending head 7 rests.

As shown in more detail in FIG. 3, that is an enlarged bending head 7, the bending head 7 is provided with a die 8 that is equipped with a clamping mechanism 9. The clamping mechanism 9 is the subject-matter of another patent application of the same Applicant. The bending head 7 is slidingly mounted on the step 6 by means of guides 10 that are horizontally located on the same step. The bending head 7 contacts an abutment member 11 which is fixed to the front frame 3 of the load bearing structure 1. The abutment member 11 makes a transversal sliding coupling between the load bearing structure 1 and the bending head 7.

A bending mandrel 12, which is mounted on an end of a mandrel rod 13, is not further described as it is the subject-matter of a previous patent application of the same Applicant. A pipe T to be bent is positioned on the bending mandrel 12. The pipe T is sustained on a mandrel holder 14 of a known kind, which is shown in FIG. 1 but is not represented in FIGS. 2 and 3 for clarity sake.

The extractor 2 is best shown in FIG. 4, that is an enlarged detail of the left-hand end of the machine. The extractor 2 is of a known kind and then not further described. However, the extractor is not cantilevered on the workbench, like in the existing bending machines, but according to the invention the extractor is located in a through manner in an anchoring plate 15. The anchoring plate 15 of the extractor 2, which is suitably strengthened by a stiffening rib 16, is fixed to a rear frame 17 as a rear portion of the load bearing structure 1, in such a way that a restraining force, which is exercised by the extractor 2 against the traction force applied by the die 8, is discharged only on the load bearing structure 1. Then advantageously the load bearing structure 1 has the rear frame 17 that surrounds the extractor 2 at least in large part but preferably totally. For this reason it is particularly suitable that the rear portion of the load bearing structure is configured as a frame like the front frame 3.

In this first embodiment of the present invention, the load bearing structure 1 of the pipe bending machine with bending mandrel is prismatic or box-shaped. The load bearing structure 1 has side walls 18, 19, 20, 21. Lifting sleeves, indicated as 22, are shown. In FIGS. 1, 2, 4 openings to enter the load bearing structure 1 are generally designed as 23.

As seen below, some parts of the load bearing structure 1, for example, which are related to the side walls, can be removed. However, all the co-operating parts of the load bearing structure are supposed to be subjected to compression in order to oppose the traction force applied by the die in a pipe bending operation. In other words, the resultant of the traction forces applied by the bending head and the resultant of the restraining forces exercised by the extractor 2, which have an axis g of the mandrel rod 13 as a direction of application, pass inside a profile being defined by the front frame 3 and the rear frame 17 of the load bearing structure 1, as the profile of the load bearing structure 1 contains inside the mandrel rod 13. Such resultants of forces transmitted through the mandrel rod 13 determine a compression stress on the load bearing structure 1. However, the load bearing structure 1 has a geometrical cross section having a centre somewhat far from the axis g of the mandrel rod where the existing forces are transmitted.

In fact, usually, in order to allow pipes to be bent according to an arc of 180° with a reduced bending radius, the mandrel 12 with the unit that supports it, and then the pipe T, are not positioned centrally inside the box-shaped load bearing structure 1. It is evident that, when a traction force is applied by the die on the pipe T, the resultant of the opposite forces exercised by the box-shaped structure, does not have a direction usually coinciding with that of the traction force.

For explanatory purpose, reference is made to FIG. 5, which is a transversal cross section of the load bearing structure 1, in its first box-shaped embodiment. The transversal cross section is substantially rectangular, and it can be pointed out that the geometrical centre of the cross section, i.e. the centre C, is not coincident with a point G that represents the intersection point of the axis g of the mandrel rod 13 in the cross section in exam.

In order to make the direction of the resultant of the applied forces coincident with the resultant of the resistant forces in the load bearing structure 1, the moment of inertia of the resistant cross section can be modified, for example applying a strengthening plate 24 in order to make the centre of inertia coincident with the intersection point G of the axis g of the mandrel rod 13.

Referring to FIG. 6 a second embodiment of a load bearing structure which is particularly resistant to the working stresses is shown in a perspective view which is longitudinally cross-sectioned by a vertical symmetry plane passing through the axis g. In this figure and in the following ones the same reference numerals are used for indicating same or similar parts. The load bearing structure in the second embodiment is round tubular and is indicated as 25, and has a front frame 3 and rear frame 17 like in the first embodiment. If the extractor 2 is positioned centrally inside the load bearing structure, the load bearing structure reacts in such a way to balance, above all, the stress applied on the pipe to be bent as the force applied on the pipe by means of bending head is discharged on the round tubular structure through the vertical rest of the bending head 7 on the front frame 3.

In this case an only axial load is distributed on all the resistant section of the load bearing structure without generating great deformations and vibrations of the load bearing structure so that defects are caused in a work subjected to a bending operation.

Referring to FIG. 7 a third embodiment of a load bearing structure according to the present invention is shown in a perspective view which is longitudinally cross-sectioned by a vertical symmetry plane passing through the axis g. The load bearing structure of the third embodiment is generally reticular and is indicated as 26, and has a front frame 3 and rear frame 17 like in the first embodiment. If the extractor 2 is positioned centrally inside the load bearing structure, the load bearing structure reacts in such a way to balance, above all, the stress applied on the pipe to be bent as the force applied on the pipe by means of bending head is discharged on the reticular structure through the vertical rest of the bending head 7 on the front frame 3. The resistant parts of the reticular structure, that are substantially beams indicated generally as 27, which are positioned in the corners of the structure, form a framework, and walls can be not present. An wall portion 28 can act as the straightening plate 24, which is described in the first embodiment and shown in FIG. 5.

Reinforcements and stiffening ribs for the beams 27 are desirable in order to obtain a uniform reaction of the load bearing structure 26, which is shown more in detail in the general perspective view in FIG. 8, where the pipe bending machine with bending mandrel is not represented for clarity sake. As seen in FIG. 8, there are supporting elements 29 for guides 10 for resting and sliding the bending head, and a milled zone 30 on which the abutment member 11 for the bending head 7 is mounted.

From above it should be understood that the load bearing structure according to the invention can have solid side walls, as in the first and second embodiment, or non continuous, when it has a framework and reticular side walls, as in the third embodiment. Of course, the load bearing structure would also have a different polygonal transversal cross section. If the cross section is round, it can be circular or oval.

In any case it is suitable that the load bearing structure has a transversal cross section having a momentum of inertia such that the traction force applied by means of the die has a direction passing through the centre of inertia of the transversal cross section.

By virtue of the fact that the system of the existing forces in the bending operation is such to generate stresses of sole compression, it is sufficient that the load bearing structure rests simply on the floor without any anchoring to the latter.

A further advantage is given by the fact that the bending head is slidable mounted in said front end on guides horizontally positioned on a step resting on the soil transversally to the longitudinal direction, the bending head being in contact with an abutment member in the front end of the load bearing structure, the abutment member making a sliding coupling with the front end of the load bearing structure. In such a way, useless flexing stresses to the load bearing structure near the bending head are avoided.

The advantages of the load bearing structure according to the present invention are even more. It should be understood that, thanks to an optimum use of the metal material that works to compression, the load bearing structure of the described kind allows the manufacturing costs of a pipe bending machine to be reduced, as a minor quantity of material is requested with respect to the existing pipe bending machine.

A further advantage is represented by the fact that the load bearing structure according to the invention is more able to undergo changes in its length if relevant extension pipes have to be worked. In fact, in the bending machine with bending mandrel of the prior art, if the length of the workbench is increased, also the deformations being caused by the flexion in the working process are increased. On the contrary, with the load bearing structure of the present invention, if the workbench increases in its length, it does not undergo perceptible deformation increases. As a positive consequence, in a concept of modular use, a section of a load bearing structure needs to be added in order to increase the length of the workbench and allow bending operations of pipes having a desired length.

In the preceding description illustrative and not limiting embodiments of the invention have been given, which is defined in the enclosed claims. 

1. A pipe bending machine with bending mandrel having a load bearing structure which is particularly resistant to working stresses, in which an extractor (2) is fixed in a rear portion of the pipe bending machine and mandrel rod (13) extends with its longitudinal axis (g), from the extractor beyond a front portion of the machine, where a bending head (7) which is provided with a die (8) stresses a pipe (T) to be bent, which is inserted in a mandrel (12), by a traction resultant force that is transmitted along the mandrel rod (13) to the extractor (2) that counteracts with a resultant restraining reaction, characterised in that the pipe bending machine comprises a load bearing structure (1; 25; 26) having a profile such that it contains inside the longitudinal axis (g) of the mandrel rod (13), in such a way that the load bearing structure (1; 25; 26) is subjected mainly to compression stresses.
 2. Machine according to claim 1, characterised in that said load bearing structure (1) is prismatic.
 3. Machine according to claim 1, characterised in that said load bearing structure (25) has a round transversal cross section.
 4. Machine according to claim 1, characterised in that said load bearing structure (26) is a reticular structure.
 5. Machine according to claim 1, characterised in that said load bearing structure (1; 25; 26) has a transversal cross section with a momentum of inertia such that the traction force applied by means of the die (8) has a direction passing through the centre of inertia of the transversal cross section.
 6. Machine according to claim 1, characterised in that said load bearing structure (1; 25; 26) rests on a floor through front and rear resting elements (4, 5).
 7. Machine according to claim 1, characterised in that said bending head (7) is slidable mounted in said front end on guides (10, 10) horizontally positioned on a step (6) resting on the soil transversally to the longitudinal direction of the machine, the bending head (7) being in contact with an abutment member (11) in the front portion of the load bearing structure (1; 25; 26).
 8. Machine according to claim 7, characterised in that the abutment member (11) forms a transversal sliding coupling. 